1. Field of the Invention
The present invention is directed to an improved method for the production of epitaxial layers on a monocrystalline substrate by shifting a slide in one direction to move a melt onto a surface of the substrate, depositing a monocrystalline epitaxial layer of material from the melt onto the surface of the substrate and subsequently moving the slide in said one direction to remove the remaining portion of the melt.
2. Prior Art
In order to produce specific semiconductor components, for example, luminescent diodes or laser diodes, it is necessary to epitaxially deposit one or more layers of semiconductor material upon a semiconductor crystal. To accomplish this, a "liquid-phase-slide epitaxy" technique or process is used and is particularly useful for the production of semiconductor components consisting of intermetallic III-V compounds and alloys thereof. In this method, a slide is used to move the melt containing the material to be deposited onto the surface of the substrate and then a layer of the material is deposited on the surface by a slight cooling of the melt. As soon as the layer thickness is deposited, the remaining melt with the aid of the slide is moved away from the substrate surface and the grown epitaxial layer that was deposited thereon. A slide-epitaxy-process of the above mentioned type and a device for accomplishing or executing this process is described in U.S. Pat. No. 3,753,801.
In the production of heterostructure laser diodes, it is necessary to epitaxially deposit a plurality of layers one upon the other. These layers differ in their composition for example the aluminum content in the case of a GaAs-(GaAl)As layer sequence. One of the factors, which determines the properties of the laser diode of this type, is the sharp change in the composition at the heterojunction between the two epitaxial layers. A laser diode having good optical and electrical properties necessitates extremely sharp heteroboundaries. In the conventional slide epitaxy process, undefied heteroboundaries occur due to the fact that during the shifting away of a melt for the Ga.sub.1-x Al.sub.x As layer wherein 0 .ltoreq. x .ltoreq. 1, the melt is not completely removed from the grown epitaxial GaAlAs layer and a slight residue of the melt is left thereon. This melt residue, which remains on the surface of the deposited epitaxial layer, will become mixed with the new GaAs melt, which is subsequently applied for deposition of the next epitaxial GaAs layer. This results in a graded heterojunction between the Ga.sub.1-x Al.sub.x As layer and the GaAs layer, e.g. the aluminum content does not drop abruptly to 0 but requires a range of 0.1 to 0.3 .mu.m to decrease or change from x amount to a 0 amount. Poorly defined heterojunctions of this type lead to considerably straying threshold current densities and a low (differential) external efficiency.